Intent to Implement and Ship: Timer throttling for hidden cross-origin frames
Sami Kyostila
Contact emails
Spec
Discussion at WICG: https://github.com/WICG/interventions/issues/9
Design doc: https://docs.google.com/document/d/1Xa8sd2M_Eh6hGSWeKTy_akzKdxcVZjCk4PQMqV8yXXw/edit#
Summary
As an intervention we want to limit the rate at which timers in out-of-view, cross-origin frames are able to fire.
Motivation
Until very recently it wasn't possible for script authors to easily determine whether their content was visible to the user or not. A common pattern therefore is to use a continuous setTimeout() loop for driving animations without considering visibility, which can be very costly for performance.
Most modern browsers already intervene to lower the update rate of timers in background tabs (e.g., 1 Hz in Chromium). We propose to extend this intervention to cross-origin iframes that are outside the visual viewport in a foreground tab. This helps to conserve power and reduce input jank caused by third party content.
Interoperability and Compatibility Risk
A potential compatibility risk is that a site can observe timers firing out-of-order if the they are scheduled from a mix of visible and hidden frames. To reduce this risk, we propose to only throttle timers in cross-origin frames.
Safari 9 ships a similar intervention which throttles timers in all out-of-view frames (instead of only cross-origin ones).
Edge is also investigating throttling timers in cross-origin frames.
There is a Firefox bug to do something similar, although so far Firefox only throttles the requestAnimationFrame API in out-of-view frames.
Ongoing technical constraints
None.
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?
Yes.
Demo link
OWP launch tracking bug
Link to entry on the feature dashboard
https://www.chromestatus.com/feature/5701844080787456
Requesting approval to ship?
Yes.
Chris Harrelson
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